The invention relates to a brake lining and more specifically to brake lining for partial lining disc brakes.
Large-surface brake linings, for example, rail vehicle disc brakes, have no even approximately constant surface pressure on their friction surface during high-energy braking operations. This is, among others, the result of a non-uniform introduction of force from the brake application device, for example, when dovetail guides are used. It also results from accidentally warmer areas of the surfaces of the lining and the brake disc, because of the thermal expansion of the friction materials, bulge out of their surfaces, in which case these areas are more stressed and, as the braking progresses, therefore become hotter than the adjacent zones. The result of such "hot spots" on the disc and the lining are premature hot cracks on the disc and lining damage because of thermal overloading. Particularly, with respect to hard lining materials (resin-bound materials, metallic sintered materials), the above-mentioned occurrence is extremely pronounced.
For avoiding the above-mentioning disadvantages--mainly when sintered materials are used--brake linings were used which have elastically disposed individual elements (German Patent Document DE-OS 43 01 006). However, in the case of such arrangements, essentially two disadvantages are found: The surface pressures on the individual elements are still not constant; they are a function of the compression corresponding to the respective surface constant of the elastic bedding of the individual elements. In addition, the lining expenses on the whole are very high and therefore result in high costs. The price is four to six times higher than organically bound, one-piece linings.
In the case of a known brake lining of this type (CA-2120392), support plates supporting lining elements are swivellably arranged on a support body in the form of a support plate. The lining elements are in each case rigidly connected with the support plate which, in turn, is riveted to the support plate. Three lining elements respectively are situated in the three corners of such a support plate which has the shape of a triangle. The rivets, which are used for connecting the support plate with the carrying plate, are in each case placed in the center area of the three legs of the triangular support plate so that the free corners of the support plate can carry out pitching movements with respect to the carrying plate to a limited extent. For this purpose, the support plates are provided with weakenings in their center. Because of such a geometry of the positioning of the lining elements and of the fastening of the support plate on the actual carrying plate, the swivel angle as well as the swivel direction of the lining elements is given within a narrow scope; that is, the swivel axis of each lining element remains generally constant. Despite the weakenings situated in the center of the support plates, a certain interdependence of the movements of one lining element with respect to the next one is to be accepted because swivel movements in one corner can be transferred beyond the center of the support plate to the area of the respective adjoining two lining elements. The result are undesirable oblique positions of the lining elements, that is, reactions of a lining element with respect to a track on the brake disc are partially also transmitted to the closest lining elements. In addition, by means of the lining elements, no equal-surface grinding pattern can be achieved because the swivel angles or rotating angles are fixed. The result are "hot spots" on the brake disc because resilient restoring forces, as increased reaction forces, can lead to temperature increases on the disc.
Based on the above, it is an object of the invention to develop a brake lining of the above-mentioned type by constructionally simple devices such that the surface pressure on the friction surface of the brake disc can be rendered more uniform. A clearly defined distribution of the overall brake application force to the individual lining elements is to be permitted. For saving expenses, it must also be possible to exchange the brake linings or parts thereof at reasonable cost.
The objects are achieved by dividing the whole lining into several lining elements or group elements and as the result of the bearing of the lining elements or group elements on a bearing body, including the fixing of the introduction of the brake application force, a uniform distribution of this brake application force to a plurality of individual lining elements or lining blocks is made possible. In addition, the lining elements or group elements form small exchangeable units, which constitutes a significant reduction of price in contrast to conventional brake linings with a dovetail guide. In the case of lining elements arranged symmetrically with respect to the center line of the bearing body (lining support or lining holder) or lining groups formed of lining elements, the division of the overall lining into two half linings is possible, in which case one lining element per support plate can be provided as the smallest lining unit. The lining elements or the groups formed by them (group elements) with the support plate carrying them can be arranged either on a common lining support or directly on the lining holder. The type of the bearing of the lining elements on the support plates, the type of the bearing of the support plates on their support, the lining support or the lining holder as well as the type of the introduction of the brake application forces with respect to the formed centers of gravity are responsible for rendering the surface pressure uniform. Preferably, the bearing of each individual element, thus of each lining block on the support plate, consists of the pairing of a ball socket with a universal ball joint which is constructed such that the resulting force consisting of the contact pressure force on the brake lining and the friction force perpendicularly thereto is in each case perpendicular to the spherical surface existing on the ball socket. In this case, the resultant force extends through the center of gravity of the surface of the respective lining element in the area of the friction on the brake disc. When the surface pressure on the overall lining is rendered uniform, thus the loading of the brake disc is more uniform, a higher energy absorption of the disc is permitted when the temperature limit is reached. The wear is also lower because the wear rises superproportionally with the temperature and, when the temperature is rendered uniform or reduced, a reduction of the wear is achieved. Naturally, when the surface pressure is rendered uniform and the brake disc loading is more uniform, the danger of the formation of hot cracks is also reduced.
Another important advantage of brake linings of the above-mentioned type are the much more favorable operating costs since the individual lining elements or group elements formed of lining elements are considerably less expensive than the previously used dovetail lining elements in the element construction or overall construction. While, in the case of one-piece brake linings of the known type but also in the case of newer multi-part brake linings, it is required to exchange during a lining exchange also the comparatively expensive lining support, because of the division into lining groups or individual elements, in each case supported by a low-cost support plate, it is possible to reuse the lining support after another fitting with lining elements or lining element groups. In their overall arrangement, the lining elements preferably form a ring sector surface which is advantageous with respect to the braking geometry, whereby a lower concave running slope of the disc must be accepted. The friction elements or lining elements may have a circular shape, but may also have a polygonal form. In addition, they may have torsional resistances or may be shaped such that they mutually support each other in a locking manner against torsion.
In an advantageous further development, three individual elements respectively can be combined to form a common lining element, which is useful in the case of rubber-based organic lining materials. It is possible to fasten the lining elements in a multiple and articulated manner on their direct support, that is, on the support plate; thus, by means of riveted joints, weld point connections, screwed connections, etc. The targeted introduction of the brake applications forces on a brake lining of the type to be used is of special significance. Thus, the introduction of loads from the brake application device can take place by a ball joint, specifically in each case in the center of gravity of a half-lining. It is also possible to introduce the overall brake application force by way of a balance arm which distributes the brake application force from a common lever uniformly to both half-linings.
In the case of one-piece support plates as lining supports for the lining elements or group elements, a certain swivellability is possible in the area of the common center line of the support, for example, as a result of a weakening of the material. This ensures that the lever forces pressing in the center of gravity of the two half-linings are uniformly distributed on the triangle points or centers of gravity of the individual or group elements (statically determined resolution of forces).
Advantageous developments and further developments are listed in additional claims.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.